I found it and this was the whole thing. There were no terms and conditions at the bottom or anything. Sorry. The funny part is the "if you have earned miles in the last 12 months....". The implication is that then they will never expire, or not with a start date of 10Jan, or 10Jan24???? Or is that if you have not flown in the prior year, then all your miles get wiped out on the 10th.

Attention FRONTIER MILESsm members:
Mile expiration resumes January 10th 2023. To keep your miles from expiring, simply earn more! We have teamed up with the following partners to give you more ways to earn, take action now to save:

If you've earned miles in the last 12 months, your miles will not expire.

You can always earn miles when you fly with Frontier and explore amazing destinations.